Lesson Plan: Loudness Physics • 9th Grade

This lesson plan includes the objectives, prerequisites, and exclusions of the lesson teaching students how to relate the loudness of sounds in decibels to the intensity of sound waves.


Students will be able to

  • recall that loudness is a quantity proportional to intensity of sound,
  • recall that loudness can be measured in the unit decibel (dB),
  • recall that a sound of loudness 𝐿dB and a frequency of 1 kHz is defined to have a loudness of 𝐿 phons,
  • recall that the intensity of sound that is at the threshold of human audibility can be defined as being 0 phons and that this is equivalent to a sound intensity of 10 W/m2,
  • apply in all combinations the formula 𝐿=10𝐼10log to a sound that has a loudness of 𝐿 phons and an intensity of 𝐼W/m2.


Students should already be familiar with

  • qualitative particle models of sound waves,
  • the inverse square law.


Students will not cover

  • calculation of sound pressure level,
  • loudness weighting.

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